Module and method for producing extreme ultraviolet radiation

ABSTRACT

A module for producing extreme ultraviolet radiation includes a supply configured to supply droplets of an ignition material to a predetermined target ignition position and a laser arranged to be focused on the predetermined target ignition position and to produce a plasma by hitting such a droplet which is located at the predetermined target ignition position in order to change the droplet into an extreme ultraviolet producing plasma. Also, the module includes a collector mirror having a mirror surface constructed and arranged to reflect the radiation in order to focus the radiation on a focal point. A fluid supply is constructed and arranged to form a gas flow flowing away from the mirror surface in a direction transverse with respect to the mirror surface in order to mitigate particle debris produced by the plasma.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-In-Part of co-pending U.S. patentapplication Ser. No. 12/078,663, filed Apr. 2, 2008, and also claimspriority to U.S. Provisional Patent Application No. 60/935,643, filedAug. 23, 2007; U.S. Provisional Patent Application No. 61/136,148, filedAug. 14, 2008; and U.S. Provisional Patent. Application No. 61/136,145filed Aug. 14, 2008. The contents of these applications are herebyincorporated in their entirety by reference.

FIELD

The present invention relates to a module and a method for producingextreme ultraviolet radiation. The module and the method can be appliedin a lithographic apparatus and a method for manufacturing a device.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.including part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

In order to be able to project ever smaller structures onto a substrate,it has been proposed to use extreme ultraviolet radiation having awavelength within the range of 10-20 nm, preferably within the range of13-14 nm.

In order to produce such radiation, a plasma may be produced by focusinga laser at a droplet, thereby changing the droplet, preferably tindroplets, into an extreme ultraviolet radiation producing plasma. Often,a so-called collector mirror may be used to focus the radiation in afocal point.

In addition to extreme ultraviolet radiation, the plasma generallyproduces debris in the form of particles, such as thermalized atoms,ions, neutrals, nanoclusters, and/or microparticles. The debris maycause damage to the collector mirror and other optics. In order toprevent the debris from causing damage, a buffer gas may be used in thevicinity of the plasma in order to mitigate the debris. Still, it hasbeen found that the collector mirror degrades and deforms when theextreme ultraviolet radiation is being produced.

SUMMARY

It is desirable to prevent the deformation and degradation of thecollector mirror.

According to an aspect of the invention, there is provided a module forproducing extreme ultraviolet radiation including a supply configured tosupply one or more droplets of an ignition material to a predeterminedtarget ignition position; a laser arranged to be focused on thepredetermined target ignition position and to produce a plasma byhitting the droplet when it is located at the predetermined targetignition position in order to change the droplet into an extremeultraviolet producing plasma; a collector mirror having a mirror surfaceconstructed and arranged to reflect the radiation in order to focus theradiation in a focal point; and a fluid supply constructed to form a gasflow flowing away from the mirror surface in a direction transverse withrespect to the mirror surface in order to mitigate particle debrisproduced by the plasma.

According to another aspect of the invention, such a module may beincluded in a lithographic projection apparatus arranged to project apattern from a patterning device onto a substrate, and specifically insuch an apparatus including: an illumination system configured tocondition a radiation beam; a support constructed to support apatterning device, the patterning device being capable of imparting theradiation beam with a pattern in its cross-section to form a patternedradiation beam; a substrate table constructed to hold a substrate; and aprojection system configured to project the patterned radiation beamonto a target portion of the substrate.

According to another aspect of the invention, there is provided a methodfor producing extreme ultraviolet radiation, wherein a radiation beam,for instance a laser beam, is focused at a droplet of an ignitionmaterial, the droplet being located at a predetermined target ignitionposition in order to change the droplet into an extreme ultravioletradiation producing plasma; reflecting the radiation using a collectormirror having a mirror surface in order to focus the radiation in afocal point; and providing a gas flow flowing away from the mirrorsurface in a direction transverse with respect to the mirror surface inorder to mitigate particle-debris produced by the plasma.

According to an aspect of the invention, there is provided a module forproducing extreme ultraviolet radiation, including a fuel supplyconfigured to supply an ignition material to a desired positionproximate an axis within a chamber; a radiation source configured tooutput a radiation beam, the radiation beam directed to the desiredposition so as to irradiate the ignition material to form a plasma thatis configured to emit an extreme ultraviolet radiation; a collectormirror including a mirror surface positioned within the chamber, themirror surface constructed and arranged to reflect and focus the extremeultraviolet radiation on a focal point positioned proximate the axis;and a fluid supply constructed to supply a gas flow along a direction ofthe axis to mitigate particle debris produced by the plasma.

According to an aspect of the invention, there is provided a method forproducing extreme ultraviolet radiation, the method includingirradiating an ignition material with a radiation beam to form a plasmathat is configured to emit an extreme ultraviolet radiation; reflectingand focusing the extreme ultraviolet radiation using a collector mirrorthat includes a mirror surface at a focal point; and supplying a gasflow that flows away from the mirror surface in a directionsubstantially transverse with respect to the mirror surface to mitigateparticle debris produced by the plasma.

In an aspect of the invention, there is provided a module for producingextreme ultraviolet radiation, the module including an extremeultraviolet radiation-emitting source, the source being provided with asupply configured to supply a fluid of an ignition material to apredetermined target ignition position and a target-igniting mechanismconstructed and arranged to produce a plasma from the ignition materialat the target ignition position, the plasma emitting the extremeultraviolet radiation; a collector mirror constructed and arranged tofocus radiation emitted by the plasma to at a focal point; and a heatsink having a thermal energy-diverting surface constructed and arrangedto divert thermal energy away from the target ignition position, whereinthe heat sink is located at a position proximate the target ignitionposition.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIG. 2 depicts a schematic view of a module according to an embodimentof the invention;

FIG. 3 is a front view of a collector of a module according to anembodiment of the invention;

FIG. 4 is a side view of the collector of FIG. 3;

FIG. 5 is a side view of a module according to an embodiment of theinvention;

FIGS. 6 and 7 show a module according to an embodiment of the invention;

FIG. 8 is a heat sink of the module of FIG. 6; and

FIG. 9 is a heat sink of the module of FIG. 7.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus includes: an illuminationsystem (illuminator) IL configured to condition a radiation beam B (e.g.EUV radiation); a support structure or patterning device support (e.g. amask table) MT constructed to support a patterning device (e.g. a mask)MA and connected to a first positioner PM configured to accuratelyposition the patterning device in accordance with certain parameters; asubstrate table (e.g. a wafer table) WT constructed to hold a substrate(e.g. a resist-coated wafer) W and connected to a second positioner PWconfigured to accurately position the substrate in accordance withcertain parameters; and a projection system (e.g. a refractiveprojection lens system) PS configured to project a pattern imparted tothe radiation beam B by patterning device MA onto a target portion C(e.g. including one or more dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure holds the patterning device in a manner thatdepends on the orientation of the patterning device, the design of thelithographic apparatus, and other conditions, such as for examplewhether or not the patterning device is held in a vacuum environment.The support structure can use mechanical, vacuum, electrostatic or otherclamping techniques to hold the patterning device. The support structuremay be a frame or a table, for example, which may be fixed or movable asrequired. The support structure may ensure that the patterning device isat a desired position, for example with respect to the projectionsystem. Any use of the terms “reticle” or “mask” herein may beconsidered synonymous with the more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a reflective type (e.g. employinga reflective mask). Alternatively, the apparatus may be of atransmissive type (e.g. employing a transmissive mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more mask tables). In such“multiple stage” machines, the additional tables may be used inparallel, or preparatory steps may be carried out on one or more tableswhile one or more other tables are being used for exposure.

The lithographic apparatus may also be of a type wherein at least aportion of the substrate may be covered by a liquid having a relativelyhigh refractive index, e.g. water, so as to fill a space between theprojection system and the substrate. An immersion liquid may also beapplied to other spaces in the lithographic apparatus, for example,between the mask and the projection system. Immersion techniques arewell known in the art for increasing the numerical aperture ofprojection systems. The term “immersion” as used herein does not meanthat a structure, such as a substrate, must be submerged in liquid, butrather only means that liquid is located between the projection systemand the substrate during exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BD (notshown in FIG. 1) including, for example, suitable directing mirrorsand/or a beam expander. In other cases the source may be an integralpart of the lithographic apparatus, for example when the source is amercury lamp. The source SO and the illuminator IL, together with thebeam delivery system BD if required, may be referred to as a radiationsystem.

The illuminator IL may include an adjuster AD (not shown in FIG. 1) foradjusting the angular intensity distribution of the radiation beam.Generally, at least the outer and/or inner radial extent (commonlyreferred to as σ-outer and σ-inner, respectively) of the intensitydistribution in a pupil plane of the illuminator can be adjusted. Inaddition, the illuminator IL may include various other components, suchas an integrator IN (not shown in FIG. 1) and a condenser CO (not shownin FIG. 1). The illuminator may be used to condition the radiation beam,to have a desired uniformity and intensity distribution in itscross-section.

The radiation beam B is incident on the patterning device (e.g., maskMA), which is held on the support structure (e.g., mask table MT), andis patterned by the patterning device. After being reflected by thepatterning device (e.g. mask) MA, the radiation beam B passes throughthe projection system PS, which focuses the beam onto a target portion Cof the substrate W. With the aid of the second positioner PW andposition sensor IF2 (e.g. an interferometric device, linear encoder orcapacitive sensor), the substrate table WT can be moved accurately, e.g.so as to position different target portions C in the path of theradiation beam B. Similarly, the first positioner PM and anotherposition sensor IF1 can be used to accurately position the patterningdevice (e.g. mask) MA with respect to the path of the radiation beam B,e.g. after mechanical retrieval from a mask library, or during a scan.In general, movement of the support structure (e.g. mask table) MT maybe realized with the aid of a long-stroke module (coarse positioning)and a short-stroke module (fine positioning), which form part of thefirst positioner PM. Similarly, movement of the substrate table WT maybe realized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the support structure (e.g. mask table) MT may beconnected to a short-stroke actuator only, or may be fixed. Patterningdevice (e.g. mask) MA and substrate W may be aligned using maskalignment marks M1, M2 and substrate alignment marks P1, P2. Althoughthe substrate alignment marks as illustrated occupy dedicated targetportions, they may be located in spaces between target portions (theseare known as scribe-lane alignment marks). Similarly, in situations inwhich more than one die is provided on the patterning device (e.g. mask)MA, the mask alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the support structure (e.g. mask table) MT and thesubstrate table WT are kept essentially stationary, while an entirepattern imparted to the radiation beam is projected onto a targetportion C at one time (i.e. a single static exposure). The substratetable WT is then shifted in the X and/or Y direction so that a differenttarget portion C can be exposed. In step mode, the maximum size of theexposure field limits the size of the target portion C imaged in asingle static exposure.

2. In scan mode, the support structure (e.g. mask table) MT and thesubstrate table WT are scanned synchronously while a pattern imparted tothe radiation beam is projected onto a target portion C (i.e. a singledynamic exposure). The velocity and direction of the substrate table WTrelative to the support structure (e.g. mask table) MT may be determinedby the (de-)magnification and image reversal characteristics of theprojection system PS. In scan mode, the maximum size of the exposurefield limits the width (in the non-scanning direction) of the targetportion in a single dynamic exposure, whereas the length of the scanningmotion determines the height (in the scanning direction) of the targetportion.

3. In another mode, the support structure (e.g. mask table) MT is keptessentially stationary holding a programmable patterning device, and thesubstrate table WT is moved or scanned while a pattern imparted to theradiation beam is projected onto a target portion C. In this mode,generally a pulsed radiation source is employed and the programmablepatterning device is updated as required after each movement of thesubstrate table WT or in between successive radiation pulses during ascan. This mode of operation can be readily applied to masklesslithography that utilizes programmable patterning device, such as aprogrammable mirror array of a type as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

FIG. 2 depicts a schematic view of a module 1 configured to produceextreme ultraviolet radiation according to an embodiment of theinvention. The module 1 may suitably serve as the source SO and providethe radiation beam to the illuminator IL. The module 1 includes a supply(e.g. fluid supply) 2 configured to supply one or more droplets 4 of anignition material to a predetermined target ignition position TIP. Also,a radiation source, e.g. a laser or laser source 6 is included in themodule 1, the laser 6 being arranged to generate a beam that is focusedonto the predetermined target ignition position TIP so as to produce anextreme ultraviolet producing plasma 8 by hitting a droplet 4 which islocated at the predetermined target ignition position TIP. In anembodiment, the droplet may be located proximate an axis of the chamber.The module 1 further includes a chamber 10 including a collector mirror12 that includes a mirror surface 14 constructed and arranged to reflectthe radiation in order to focus the radiation on a focal point FP and afluid supply 16 constructed to form a gas flow GF flowing away from themirror surface 14 in a direction D transverse with respect to the mirrorsurface 14 in order to mitigate particle debris produced by the plasma.

The particle debris mitigation preferably occurs using the Pécleteffect. The so-called Péclet number describes the rate of advection of aflow to its rate of diffusion, often thermal diffusion. It is equivalentto the product of the Reynold number and the Prandtl number in the caseof thermal diffusion, and the product of the Reynolds number and theSchmidt number in the case of mass dispersion. By creating a flow suchthat its advection is sufficiently high, the Péclet number becomes sohigh such that the particle debris reaching the collector mirror will besufficiently low. Suitable speeds for the gas flow may be found above aspeed of about 5 m/s. At speeds of about 5 m/s and higher, hydrides,such as SnH₄ may be transported away from the collector mirror surface14. Typically, the speed for the gas flow may be about 100 m/s.

In an embodiment, the focal point may be positioned proximate the axis.The axis may be an optical axis. The gas flow GF may be continuouslysupplied by the apertures 18 during generation of the plasma.

As heat load of a more or less stationary buffer gas in the vicinity oftarget ignition position may cause deformation and degradation of thecollector mirror, a gas flow is being formed when the module 1, depictedin FIG. 2, is in operation, which gas flow GF flows away from the mirrorsurface 14, thereby reducing the amount of thermal contact between thegas in the gas flow GF and the mirror surface 14.

Serving as fluid supply 16, one or more apertures 18 may be provided inthe mirror 12 each configured to allow for passage of at least a part ofthe gas flow GF. Preferably, one or more apertures 20 may be provided inthe laser 6 to allow for passage of at least a part of the gas flow GF.In another embodiment, the gas flow GF is supplied to the chamber 10with a plurality of fluid supplies (or fluid supply units) 22 arrangedin the module 1. Each fluid supply 22 is arranged to provide a subflowof gas, and each of the subflows being directed towards a centralregion, such that the gas flow, away from the mirror surface, isprovided by a collision between the subflows occurring in the centralregion.

The module 1 includes a pump 24 arranged to pump the gas out of thechamber 10. Preferably the pump 24 is controlled by a pressurecontroller 21 arranged to control the pump 24 in order to maintain thepressure at a level within a range of about 10 Pa to 400 Pa, morespecifically in a range of about 20 Pa to 200 Pa. In an embodiment, avery suitable pressure level is 100 Pa. Due to the relatively hightemperature of operation, such gas pressures may not impairtransmissivity of the system to the extreme ultraviolet radiation,especially not if the gas is hydrogen. It will be appreciated that thepressure may be controlled in another manner, for instance, bycontrolling the fluid supply 16 instead of the pump 24.

In case the module is included in a lithographic projection apparatus,such as the apparatus shown in FIG. 1, the pump 24 may serve to preventthe gas flow GF to flow into other parts of the apparatus, for exampleto the illumination system IL.

As mentioned earlier, the gas flow may include molecular and/or atomichydrogen or any other suitable gas. The gas can be supplied by fluidsupply 16 by supplying a gas. The fluid supply may also supply a liquidwhich will change to a gaseous phase upon entry into the chamber 10.

Referring to FIG. 3, an alternative is disclosed to the embodiment ofFIG. 2. The embodiment of FIG. 3 is similar to the embodiment of FIG. 2.A difference is that in the embodiment of FIG. 3, the fluid supply 2includes one or more manifolds 26 arranged at a location proximate themirror surface 14 of the collector mirror 12. The manifolds 26 areconfigured to supply the gas flow through a plurality of apertures 18.By employing the manifolds 26, which may be a structure separate fromthe collector mirror 12, there is no need to provide apertures in thecollector mirror 12. This significantly increases manufacturability ofthe module according to an embodiment of the invention.

In the embodiment of FIG. 3, the manifolds 26 are positioned in thechamber 10 such that the apertures 18 to direct the gas toward theplasma target ignition position.

FIG. 4 is a side view of the collector mirror 12 of FIG. 3. In FIG. 4,however, the laser source 6 is shown and extends through a hole 28 (seealso FIG. 3).

FIG. 5 is a side view of yet another embodiment of the module. Theembodiment of FIG. 5 is similar to the embodiment of FIG. 2. However, inFIG. 5, the module 1 additionally includes a gas collection system 30configured to collect the gas flow including at least a part of the atleast a part of the particles from the particle debris. As can be seenin FIG. 5, the gas collection system 30 is configured to collect the gasflow at a location opposite to the fluid supply relative to the targetignition position TIP. The fluid supply 16 and the gas collection systemare arranged such that the gas flow may reach a speed of about 100 m/sor any other flow speed within the range of about 10 m/s to 1000 m/s.

As can be seen in FIG. 5, the gas flow supplied by the fluid supply 16in FIG. 5 is a narrow jet. Use of the gas collection system 30 may becombined with the type of apertures 16 of the embodiments of FIGS. 2 and3 respectively. In this manner, a more homogeneous and broader gas flowcan be obtained as a background gas flow.

FIGS. 6 and 7 disclose a yet further module 101 for producing extremeultraviolet (EUV) radiation in accordance with an embodiment of theinvention. The module includes an extreme ultraviolet radiation-emittingsource, the source being provided with a supply configured to supply afluid of an ignition material to a predetermined target ignitionposition TIP. Although not shown in FIGS. 6 and 7 for the sake ofclarity, the supply may be the same or at least similar to the supply 2shown in FIG. 2.

The source may further be provided with a target-igniting mechanism 106,in the respective embodiments of FIGS. 6 and 7 a laser, constructed andarranged to produce a plasma from the ignition material at the targetignition position, the plasma emitting the EUV radiation. In this case,the source is a laser-produced plasma (LPP) source and extends through ahole in a collector mirror 112 having a mirror surface 114. Another typeof such a source is a discharge-produced plasma (DPP) source.

The collector 112 is comprised in the module 101 and is constructed andarranged to focus radiation emitted by the plasma to at a focal point FPand a heat sink 132 having a thermal energy-diverting surface 134constructed and arranged to divert thermal energy away from the targetignition position TIP. The heat sink 132 may be located at a positionproximate the target ignition position as shown in FIGS. 6 and 7.

In the embodiments of FIGS. 6 and 7, the module comprises a chamber (notshown in its entirety in the Figures) in which the source, the collectormirror 112 and the heat sink 132 are located. The chamber may containmolecular hydrogen, hydrogen radicals or a mixture thereof.

The module 101 in FIG. 6 differs from the module 101 of FIG. 7 in thatthe heat sink 132 of the module 101 shown in FIG. 7 has a cylindricalshape (see FIG. 8), while the heat sink 132 of the module 101 shown inFIG. 6 has a conical shape (FIG. 9) and tapers towards the focal pointFP. Typically the heat sink 132 may have a cross-section with a diameterof about 80 mm or about 160 mm. The opening angle of theconically-shaped heat sink 132 of FIG. 9 is about 10° or about 20° or inthe range between about 10° to 20°.

In both the embodiments of FIGS. 6 and 7, the heat sink 132 is locatedin a zone which is substantially free of radiation directed by thecollector mirror 112 to the focal point FP, because the zone is shieldedfrom reflection by the mirror surface 114 of the mirror 112 by anon-reflective part 136 in the collector mirror. This part 136 of thecollector mirror lacks reflectivity, since it is the location where thea target-igniting mechanism 106, i.e. the laser, extends through thecollector mirror 112. Thus, the heat sink 132 does not block any EUVradiation reflected by the collector mirror 112 and therefore has nodetrimental effect on the EUV radiation intensity at the focal point FP.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

Although specific reference may have been made above to the use ofembodiments of the invention in the context of optical lithography, itwill be appreciated that the invention may be used in otherapplications, for example imprint lithography, and where the contextallows, is not limited to optical lithography. In imprint lithography atopography in a patterning device defines the pattern created on asubstrate. The topography of the patterning device may be pressed into alayer of resist supplied to the substrate whereupon the resist is curedby applying electromagnetic radiation, heat, pressure or a combinationthereof. The patterning device is moved out of the resist leaving apattern in it after the resist is cured.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 355, 248, 193, 157 or 126 nm) andextreme ultra-violet (EUV) radiation (e.g. having a wavelength in therange of 5-20 nm), as well as particle beams, such as ion beams orelectron beams.

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, includingrefractive, reflective, magnetic, electromagnetic and electrostaticoptical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the invention may take the form of acomputer program containing one or more sequences of machine-readableinstructions describing a method as disclosed above, or a data storagemedium (e.g. semiconductor memory, magnetic or optical disk) having sucha computer program stored therein.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

What is claimed is:
 1. A method for producing extreme ultravioletradiation, comprising: directing a radiation beam onto a droplet of anignition material, the droplet being located at a target ignitionposition, so as to change the droplet into a plasma that is configuredto produce an extreme ultraviolet radiation; reflecting the radiationusing a collector mirror that includes a mirror surface to focus theradiation at a focal point; and providing a gas flow that is ejectedfrom a fluid supply comprising a manifold with a plurality of aperturesto eject gas, the manifold provided in front of the mirror surface or infront of an edge of the mirror surface, or both, so that said gas isprovided by the manifold to the plurality of apertures without passingthrough said collector mirror, the gas flow being ejected in a mannersuch that, upon exiting said fluid supply, said gas flow is directedtoward the target ignition position in a direction substantiallytransverse with respect to and away from the mirror surface to mitigateparticle debris produced by the plasma.
 2. The method according to claim1, wherein the radiation beam is a laser beam.
 3. The method accordingto claim 1, wherein the gas flow comprises molecular and/or atomichydrogen.
 4. The method according to claim 1, wherein the targetignition position and the mirror are located in a chamber.
 5. The methodaccording to claim 4, wherein a gas pressure in the chamber ismaintained between about 10 Pa and 400 Pa.
 6. The method according toclaim 5, wherein the gas pressure is between about 20 Pa and 200 Pa. 7.The method according to claim 1, wherein a plurality of subflows of gasare provided, each of the subflows being directed towards a centralregion of the mirror surface, such that the gas flow, away from themirror surface, is provided by collision between the subflows occurringin the central region.
 8. The method according to claim 1, wherein thegas flow that includes at least a part of the particles from theparticle debris is collected.
 9. The method according to claim 8,wherein the gas flow including at least a part of the particles from theparticle debris is collected at a location opposite to the mirrorsurface relative to the target ignition position.
 10. A module forproducing extreme ultraviolet radiation, comprising: a supply configuredto supply one or more droplets of an ignition material to a targetignition position; a radiation source configured to supply a radiationbeam arranged to be focused on the target ignition position and toproduce a plasma by hitting a droplet located at the target ignitionposition so as to change the droplet into an extreme ultravioletproducing plasma; a collector mirror including a mirror surfaceconstructed and arranged to reflect the radiation to focus the radiationat a focal point; and a fluid supply comprising a manifold with aplurality of apertures to eject gas, the manifold arranged in front ofthe mirror surface or in front of an edge of the mirror surface, orboth, so that said gas is provided by the manifold to the plurality ofapertures without passing through said collector mirror, and constructedto form a gas flow that is directed, upon exiting said fluid supply,toward the target ignition position and in a direction substantiallytransverse with respect to and away from the mirror surface to mitigateparticle debris produced by the plasma.
 11. The module according toclaim 10, wherein the gas comprises molecular and/or atomic hydrogen.12. The module according to claim 10, wherein the module comprises achamber in which the target ignition position and the mirror arelocated.
 13. The module according to claim 12, wherein the modulecomprises one or more pumps arranged to pump gas out of the chamber. 14.The module according to claim 12, wherein the module is provided with apressure controller constructed to maintain a gas pressure in thechamber between about 10 Pa and 400 Pa.
 15. The module according toclaim 14, wherein the gas pressure is between 20 Pa and 200 Pa.
 16. Themodule according to claim 10, further comprising one or more pumps,arranged to pump gas out of a chamber in which the target ignitionposition and the mirror are located and a pressure controller arrangedto control the one or more pumps in order to maintain a gas pressure inthe chamber between about 10 Pa and 400 Pa.
 17. The module according toclaim 16, wherein the gas pressure is between about 20 Pa and 200 Pa.18. The module according to claim 10, wherein the module comprises aplurality of fluid supplies each arranged to provide a subflow of gas,and each of the subflows being directed towards a central region of themirror surface, such that the gas flow, away from the mirror surface, isprovided by collision between the subflows occurring in the centralregion.
 19. A module for producing extreme ultraviolet radiation,comprising: a fuel supply configured to supply an ignition material to aposition proximate an axis within a chamber; a radiation sourceconfigured to output a radiation beam, the radiation beam directed tothe position so as to irradiate the ignition material to form a plasmathat is configured to emit an extreme ultraviolet radiation; a collectormirror including a mirror surface positioned within the chamber, themirror surface constructed and arranged to reflect and focus the extremeultraviolet radiation on a focal point positioned proximate the axis;and a fluid supply comprising a manifold with a plurality of aperturesto eject gas, the manifold arranged in front of the mirror surface or infront of an edge of the mirror surface, or both, so that said gas isprovided by the manifold to the plurality of apertures without passingthrough said collector mirror, and constructed to supply a gas flowsubstantially toward the position so that said gas flow suppliedsubstantially toward the position carries particle debris produced bythe plasma away from the mirror surface substantially along a directionof the axis and substantially toward the focal point.
 20. The moduleaccording to claim 19, wherein the gas flow flows substantially parallelto the axis.
 21. The module according to claim 19, wherein the gas flowis configured to flow away from the mirror surface and toward the focalpoint.
 22. The module according to claim 19, wherein the fluid supplyincludes a first and a second fluid supply units that are configured toproduce a first and a second sub-flow, respectively, the first and thesecond sub-flow directed toward a central region of the mirror surfaceproximate the axis to form the gas flow.
 23. The module according toclaim 19, wherein the module comprises a gas collection systemconfigured to collect the gas flow including at least a part of the atleast a part of the particles from the particle debris.
 24. The moduleaccording to claim 23, wherein the gas collection system is configuredto collect the gas flow at a location opposite to the fluid supplyrelative to the target ignition position.
 25. A lithographic projectionapparatus arranged to project a pattern from a patterning device onto asubstrate, the lithographic apparatus comprising: an illumination systemconfigured to condition a radiation beam; a support constructed to holda patterning device, the patterning device being capable of impartingthe radiation beam with a pattern in its cross-section to form apatterned radiation beam; a substrate table constructed to hold asubstrate; a projection system configured to project the patternedradiation beam onto a target portion of the substrate; and a module forproducing extreme ultraviolet radiation, the module including a supplyconfigured to supply one or more droplets of an ignition material to atarget ignition position; a radiation source configured to supply aradiation beam arranged to be focused on the target ignition positionand to produce a plasma by hitting a droplet located at the targetignition position so as to change the droplet into an extremeultraviolet producing plasma; a collector mirror including a mirrorsurface constructed and arranged to reflect the radiation to focus theradiation at a focal point; and a fluid supply comprising a manifoldwith a plurality of apertures to eject gas, the manifold arranged infront of the mirror surface or in front of an edge of the mirrorsurface, or both, so that said gas is provided by the manifold to theplurality of apertures without passing through said collector mirror,and constructed to form a gas flow that is directed, upon exiting saidfluid supply, toward the target ignition position and in a directionsubstantially transverse with respect to and away from the mirrorsurface to mitigate particle debris produced by the plasma.
 26. A methodfor producing extreme ultraviolet radiation, comprising: irradiating anignition material located at a target ignition position with a radiationbeam to form a plasma that is configured to emit an extreme ultravioletradiation; reflecting and focusing the extreme ultraviolet radiationusing a collector mirror that includes a mirror surface at a focalpoint; and supplying a gas flow that is ejected from a fluid supplycomprising a manifold with a plurality of apertures to eject gas, themanifold arranged in front of the mirror surface or in front of an edgeof the mirror surface, or both, so that said gas is provided by themanifold to the plurality of apertures without passing through saidcollector mirror, in a manner such that, upon exiting said fluid supply,said gas flow is directed toward the target ignition position in adirection substantially transverse with respect to and away from themirror surface to mitigate particle debris produced by the plasma. 27.The method according to claim 1, wherein at least part of the gas flowis supplied toward the focal point.
 28. The method according to claim 1,wherein at least part of the gas flow is directed along a same directionas the radiation.
 29. The module according to claim 19, wherein thecollector mirror is arranged upstream the position and the focal pointis positioned downstream the position.
 30. The module according to claim19, wherein, substantially along the axis, the position is between thecollector mirror and the focal point.
 31. The method according to claim7, wherein the plurality of subflows of gas are provided by fluidsupplies arranged in front of the edge of the mirror surface.